Technical Abstract:
The North Central Regional Plant Introduction Station (NCRPIS) located in Ames, Iowa maintains a large collection of diverse plant germplasm. Controlled pollination of individual accessions is necessary to preserve the original genetic diversity. Some plants, especially those with conspicuous flowers, are more effectively pollinated by insects than by hand [1]. At NCRPIS, insect pollinators are used in caged regenerations of accessions of oilseed Brassicaceae, Cucurbitaceae, wild-type Helianthus, Umbelliferae such as Daucus, aromatic plants such as Ocimum and Petroselinum, and a wide variety of ornamentals.
History of the Alfalfa Leafcutting (ALC) bee and its use at NCRPIS: ALC bees were introduced to the United States in the 1930s from southeastern Europe [2]. Traditionally, ALCs were utilized for pollination of forage legumes; NCRPIS staff used them for this purpose in the mid-1980s. More recently, it was discovered ALCs would successfully pollinate blueberries (Vaccinium) [3]. Beginning in 1994 at NCRPIS, R.L. Wilson and C.A. Abel used ALCs as a comparative pollinator in field studies. Since 2004, S.J. Hanlin and S.G. McClurg have conducted tests comparing ALC as an alternate pollinator to honey bees. ALCs were selected for this purpose because cells are relatively inexpensive to purchase and manage and established rearing protocols were already in place. Also in their favor, ALCs are non-stinging, providing increased safety for staff working in cages, and they require minimal attention once placed in cages. From these tests, it was determined ALCs would pollinate a wide variety of plant taxa maintained at the NCRPIS.
Investigation 1: Can ALCs be used as a general pollinator at NCRPIS ?
We were searching for an alternate pollinator to supplement the other insect pollinators used at NCRPIS; personnel at the Bee Biology and Systematics Laboratory at Logan, Utah reviewed our efforts and recommended trying the ALC bee. In 2004, we compared pollination efficacy of ALC to honey bees on five accessions of cucurbits, two accessions of Brassica, and one Erysimum. Analysis of seed production showed no significant difference between treatments or entries. We noted that ALC pollination was most successful for taxa with small to medium-sized flowers with a relatively flat surface, and when growing conditions were warm (26 C or more), mostly sunny and dry. In 2005, similar results were obtained with three accessions of cucurbits, and one accession each of Brassica, Daucus, and Ocimum. We found that ALCs were not successful at pollinating large deep flowers, such as Cucurbita pepo, nor were they very productive in dark, cool, wet conditions. Other plant genera for which ALC pollinations have proved unsuccessful are Hypericum (possibly due to the hypericin component known to have insecticidal properties [4]) and Matricaria.
Investigation 2: Can ALC bees be emerged from cells earlier and later than normally used for plant germplasm regeneration in greenhouse cages?
Early emergence: Curatorial staff needed an effective pollinator for seed production from wild Cucumis in greenhouse cages during winter. We obtained summer-produced ALC cells in November – December and incubated them at 30 C. Bees emerged from these cells 21 to 30 days after incubation initiation; however, the percent of bees emerged was lower than expected for the normal emergence period. Shortened bee lifespan occurred due to physiological immaturity until the end of March; at that time bee lifespan began to lengthen in cages containing ALC-preferred plant material.
Late emergence: We wished to determine if ALCs could be emerged from cells which had been purchased for summer use, in order to pollinate late-blooming accessions. In 2005 and 2006, cells were incubated from September through November in order to achieve bee emergence from October into December. The percent emergence was lower than during the summer months, however the bees pollinated crops successfully. Once again bees lived only ca one weeks time, but in this case, it was due to reduced vigor from extended storage of cells.
Investigation 3: Is it necessary to provide ALC-preferred nesting plants and domiciles in regeneration cages?
Nesting plants: It was unknown if ALCs would utilize selected crop plant taxa for nesting material; extensive crop damage is undesirable. We also wanted to identify and provide the best environmental conditions for ALCs to optimize pollination. It was suggested ALCs may require specific plants for nesting. In greenhouse test cages in 2004-2005, we provided four additional plant species specifically for nesting material. Although the bees did cut leaf disks from these nesting plants, they also made use of leaves and flower petals from the crop plants in the test cages. In 2005 field cages with and without alfalfa nesting plants, no differences were noted in bee activity or crop seed production. Because there were no differences in the quantity or quality of seed produced between treatments, we did not feel it was necessary to implement the addition of nesting plants to cages.
Domiciles: When ALC bees were released to cages without domiciles in 2004, they appeared to make use of holes in cage frames in order to nest or protect themselves. In 2005-2006 studies where domiciles were provided, the bees utilized them for shelter, especially during the overnight hours or in inclement weather, and for nesting in preferred crops. Providing domiciles increased bee longevity and productivity; a standard domicile was developed for use in regeneration cages.